Sepsis, also referred to as sepsis syndrome, is a consequence of serious infection by bacteria, fungi, or viruses. Sepsis accounts for tens of thousands of deaths in the United States every year; it is a leading cause of death of patients in surgical intensive care units.
Sepsis is an inflammatory disorder in which endogenous cytokines and other bioactive molecules, produced or released in response to an inflammatory stimulus such as bacterial endotoxin (a component of the cell wall of gram-negative bacteria), cause various symptoms including fever, neutropenia, blood coagulation disorders, hypotension, shock, and organ damage.
Sepsis (or in its more severe form, septic shock), is one example of a broader class of disease called the “Systemic Inflammatory Response Syndrome” (SIRS), which is an organism's reaction to inflammatory stimuli such as endotoxin (which can be present in the bloodstream without bacteremia, e.g. due to leakage of endotoxin from gram-negative bacteria into the circulation from a localized infection or from the intestine); SIRS can also be triggered by gram-positive bacteria, fungi, viruses, and can also be a consequence of autoimmune disorders or administration of therapeutic inflammatory cytokines.
Current treatment of SIRS involves circulatory and respiratory support, but does not directly address improvement of tissue resistance to inflammatory stimuli such as endotoxin, or inflammatory mediators.
Monoclonal antibodies for neutralizing endotoxins or mediators of its physiologic effects are under development. However, it is expensive or impractical to use antibodies as prophylaxis in susceptible patients, prior to the onset of symptoms of endotoxin poisoning. Moreover, it is difficult to determine which patients are likely to benefit from antibody treatment, since the time required to culture and identify infectious organisms often exceeds the time limit for implementation of effective therapy. Similar problems have been encountered in attempts to use receptor antagonists of specific inflammatory meidators like interleukin-1.
Endotoxin toxicity is in part mediated by endogenous cytokines and other bioactive molecules released from macrophages, Kupffer cells (sessile macrophages in the liver) and other cell types in response to endotoxin. Among the most significant of these mediators are tumor necrosis factor (TNF) and interleukin-1 (IL-1). Others include platelet activating factor (PAF), interleukin-6, and leukotrienes and other arachidonic acid derivatives. Administration of these cytokines or mediators results in symptoms similar to at least some of those elicited by endotoxin. Agents or pathological conditions other than bacterial endotoxin can result in elevated production or activity of (or sensitivity to) TNF or IL-1, resulting in tissue damage. Such conditions include infection with gram-positive bacteria, viruses or fungi, or liver damage. Inflammatory cytokines can produce tissue damage if present in excess, but when elicited in moderate amounts, they are important in the defense against infectious organisms or viruses. For example, antibodies to TNF can reduce toxicity of an administered dose of endotoxin (by blocking the negative effects of TNF elicited by the endotoxin), but can have a deleterious effect in the case of some bacterial infections, converting a sublethal state of infection into an overwhelming lethal infection (Havell, J. Immunol., 1987, 139:4225–4231; Echtenacher et al., J. Immunol., 1990 145:3762–3766). Thus, there are inherent problems with strategies for treating sepsis syndrome or SIRS with agents which directly inactivate inflammatory cytokines.
The liver is a major site for clearance or detoxification of endotoxin (Farrar and Corwin, Ann. N.Y. Acad. Sci., 1966 133:668–684) and inflammatory proteins like TNF; conversely, the liver is susceptible to damage by endotoxin and its mediators. Liver damage from many originating causes (e.g. carbon tetrachloride, choline deficiency, viral infection, Reye's syndrome, alcohol) is in part mediated by bacterial endotoxin or mediators elicited by endotoxin even when symptoms of systemic sepsis are not present (Nolan, Gastroenterology, 1975, 69:1346–1356; Nolan, Hepatology, 1989, 10:887–891). Hepatic toxicity is dose-limiting in patients receiving intentional injections of endotoxin for possible efficacy in treating cancer (Engelhardt et al., Cancer Research, 1991, 51:2524–2530). The liver has been reported to be the first vital organ displaying pathological alterations in septic shock (Kang et al., J. Histochem. Cytochem., 1988 36:665–678). Moreover, hepatic dysfunction occurs in the early stages of sepsis and may initiate sequential organ failure (Wang et al., Arch. Surg., 1991, 126:219–224)
The liver is important in regulating the sensitivity of an animal to endotoxin. Various treatments which impair liver function or metabolism, such as poisoning with lead acetate, cycloheximide, Actinomycin D or galactosamine can increase the sensitivity of animals to endotoxin or TNF, in some cases by several orders of magnitude.
Galactosamine-induced liver damage is unique in that it is readily reversible during a period before cell death occurs. Galactosamine selectively depletes hepatic uridine nucleotides, by locking them into UDP-hexosamines that are not converted back into free nucleotides. This can lead to liver damage if the depletion of uridine nucleotides is sufficiently prolonged, due to impairment of RNA and protein synthesis. The biochemical deficiency induced by galactosamine is readily reversed by administration of uridine, which replenishes the uridine nucleotides trapped by the galactosamine. Thus, administration of uridine shortly before or after administration of galactosamine attenuates galactosamine-induced hepatic damage and consequently restores sensitivity to endotoxin toward normal values (Galanos et al., PNAS, 1979, 76:5939–5943).
Similarly, endotoxin hypersensitivity in mice deliberately treated with the rodent hepatotoxin TCDD was partially reversed by administration of uridine (Rosenthal et al., Toxicology, 1989 56:239–251).
However, in contrast to these situations wherein uridine partially reversed experimentally-reduced resistance to endotoxin, uridine was reported to have no protective effect in normal mice challenged with endotoxin (Markley et al., J. Trauma 1970, 10:598–607), i.e., it did not result in greater-than-normal resistance to endotoxin.
Uridine, cytidine, and orotate have been tested for effects on liver function in hepatic disorders and in experimental models, with mixed results. Shafer and Isselbacher (Gastroenterology, 1961, 40:782–784) reported that daily intravenous infusion of 25 to 100 milligrams of cytidine and uridine, for 3 to 7 days, to patients with hepatic cirrhosis had no effect on clinical status. Orotic acid added to rat diet in a concentration of 1 percent results in fatty infiltration of the liver (von Euler et al, J. Biol. Chem., 1963, 238:2464–2469); orotic acid administered by intraperitoneal injection reduced liver damage in rats treated with carbon tetrachloride, dichloroethane, DDT, and 9,10-dimethyl-1,2-benzanthracene (Pates et al., Farmakol Toksikol., 1968, 31:717–719). Lysine-orotate potentiated the toxicity of hepatotoxic extracts from the mushroom Amanita Phalloides; sodium orotate and orotic acid had no effect on Amanita extract toxicity (Halacheva et al., Toxicon, 1988, 26:571–576). Orotic acid has been administered clinically to humans for treatment of neonatal hyperbilirubinemia and for improving recovery from myocardial infarction (O'Sullivan, Aust. N.Z. J. Med., 1973, 3:417–422). Orotate is not well absorbed after oral administration, in part due to poor solubility.
Hata et al. (U.S. Pat. Nos. 4,027,017 and 4,058,601) disclose that uridine diphosphate and uridinediphosphoglucuronic acid reduce blood alcohol content and inhibit accumulation of neutral lipids in the liver after administration of ethanol.
Clinical trials involving the administration of uridine (e.g. for the purpose of attenuating host toxicity of the antineoplastic drug 5-fluorouracil) have been complicated due to the biological properties of uridine itself. Uridine is poorly absorbed after oral administration; diarrhea is dose limiting in humans (van Groeningen et al., Proceedings of the AACR, 1987, 28:195). Parenteral administration of uridine requires use of a central venous catheter (with consequent discomfort and risk of infection), since phlebitis was a problem in early clinical trials when uridine was administered via a brachial venous catheter (van Groeningen et al. Cancer Treat Rep., 1986, 70:745–50).
Administration of acyl derivatives of uridine and cytidine, which are readily absorbed from the gut into the bloodstream, and which are then hydrolyzed to yield free uridine or cytidine in the circulation, overcome the problem of poor oral absorption of the free nucleosides (U.S. patent applications Ser. Nos. 438,493, 115,929, and 903,107, hereby incorporated by reference).